In a scheme of making electronic circuits and/or devices using printing processes, one or more printing processes for printing either or both of N+ and P+ dopants may be employed (see, e.g., U.S. Pat. Nos. 7,701,011 and 7,767,520; and U.S. patent application Ser. No. 11/818,078, filed on Jun. 12, 2007. For example, the process flow may include printing of a dopant composition covering a gate/channel crossover of a transistor structure, but leaving at least part of the source/drain region(s) of the transistor structure open for contact formation. Alternatively, the process flow may include coating the entire substrate with the dopant composition, but leaving or forming via holes over areas where contacts are desired. The dopant composition being deposited may act as a dopant source for doping the underlying silicon, and optionally may also serve as a dielectric layer. Alternatively, the process flow may include coating or printing a dopant ink, doping any underlying silicon and then removing the dopant film entirely prior to depositing the next layer (e.g., an interlayer dielectric, etc.). Compositions that may be suitable for use in printing (e.g., inkjet printing) have been previously described (see, e.g., U.S. Pat. Nos. 7,422,708, 7,553,545, 7,498,015, 7,314,513, 7,485,691, 7,674,926, and 7,879,696; and U.S. patent application Ser. Nos. 11/867,587, 12/175,450 and 12/131,002, respectively filed on Oct. 4, 2007, Jul. 17, 2008, and May 30, 2008.
When printing dopant-containing inks for doping one or more underlying semiconductor films and/or features, a number of challenges can arise. For example, specific challenges in printing dopant-containing inks include (1) control over line shape (e.g., average width and width distribution, average thickness, profile such as dome v. coffee rings, etc.); (2) control over the dopant composition within the printed line; (3) maintaining a tight control over the dopant concentration (e.g., within the underlying semiconductor layer) across the printed line; (4) limited or no doping of the underlying semiconductor layer outside of the printed line; (5) limited or no reaction with other underlying layers which may be present (e.g. silicon oxide, silicon nitride, gate material, etc.); and (6) overall integration of the printed dopant, which may include controlled sheet resistance, counterdoping and/or outgassing of the dopant, compatibility of the dopant ink with other layers in device such as silicon dioxide, gate, etc.
In order to obtain tight control over the line shape, the ink composition generally requires sufficient control of the fluid mechanical properties (e.g., viscosity, rheology, surface tension, etc.) of the ink or solution used to form the printed dopant layer. Since the printed dopant layers can function as a dopant source for an underlying semiconductor structure, line shape and thickness control of the printed dopant layer may be important to ensure uniform doping of the underlying semiconductor structure and/or functionality of the feature. Excessive variability in the shape and/or thickness of a printed dopant layer may result in uneven doping of an underlying semiconductor structure. For example, a printed dopant layer having non-uniform film morphology may result in higher dopant levels in an underlying semiconductor structure where the printed dopant layer is thicker, and lower dopant levels in an underlying semiconductor structure where the printed dopant layer is thinner. This, in turn, can cause undesirable variability in the electrical characteristics of devices in different areas of the substrate.
Furthermore, curing or heating processes, which often follow printing, can cause line shape or pattern width distortion such as line waviness, spreading, or retraction. Such distortion can occur, for example, by a heat-induced width change resulting from a decreased viscosity of the printed dopant layer, and/or changes in the wetting characteristics of the printed composition due to the increased temperature. This can lead to inadvertent doping of areas not intended to be doped or covered with printed dopant ink. The consequences of such pattern waviness, spreading, or retraction may include (1) doping of areas not intended to be doped; (2) counter doping of N-type areas by P-type dopants; and/or (3) counter doping of P-type areas by N-type dopants.
These and other problems may prevent integration of printed dopant inks in an electronic device manufacturing process.